Process and apparatus for increasing vacuum tower production



O 1953 J. R. GUALA 2,658,863

PROCESS AND APPARATUS FOR INCREASING VACUUM TOWER PRODUCTION Filed July 15, 1952 5 Sheets-Sheet 1 TO CONDBINSBRS FIGLI.

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2 mass OIL Ffii ZONE Q 25 13 5 15 26 STRIPPING L 3 4,35 20M: a= STRIPPIING STEAM :51

INVENTOR. 252 JOHN GU FXLfi ins ATTORNEY Nov. 10, 1953 J. R. GUALA A PROCESS AND APPARATUS FOR INCREASING VACUUM TOWER PRODUCTION 3 Sheets-Sheet 2 Filed July 15, 1952 &%N E n r ETV q n WS m a m am s R %P m STRIPPING J HN R. GUflLA J. R. GUALA PROCESS AND APPARATUS FOR INCREASING VACUUM TOWER PRODUCTION Nov. 10, 1953 3 Sheets-Sheet 3 Filed July 15, 1952 wmmzoh AmzoHazM zoo mow Emma o nmmmmgo x85. 2:305 AmZoEBnm am OOOH - INVENTOR. J HN R ALfi n 0 Ham Patented Nov. 10, 1953 PROCESS AND APPARATUS FOR INCREAS- ING VACUUM TOWER PRODUCTION John R. Guala, Bywood, Upper Darby, Pa., as-

signor to Gulf Oil Corporation, Pittsburgh, Pa., a corporation of Pennsylvania Application July 15, 1952, Serial No. 298,986

13 Claims. (01. 202-40) This invention relates to a process and apparatus for increasing vacuum tower production and particularly to vacuum fractionation systems and methods employed in connection with the separation of thermally decomposable liquid mixtures such as hydrocarbon oils. In the fractional distillation of hydrocarbon oils and the like in a vacuum fractionating tower, feed oil heated to a high temperature is introduced into the vacuum tower. The reduced pressure at which the tower is operated and the high temperature of the oil at the time of its introduction into the tower results in instantaneous vaporization or a flashing of part of the feed oil into vapor. The resulting vapor is then passed upwardly in the tower through a fractionation or distillation zone which may comprise a plurality of bubble cap trays or equivalent elements.

In the fractionating zone the upwardly moving vapors are passed countercurrently to condensed liquid moving downwardly over the trays. Vapors not condensed during their passage through the distillation zone are removed from the top of the tower and passed through heat exchange equipment or condensing apparatus for further processing.

In most cases the vacuum producing means are employed in association with the condensing apparatus to create within the tower the reduced pressure necessary for the operation of the vacuum tower.

The passage of vapor from the tower flash zone up through the fractionating trays results in a substantial pressure drop between the vacuum producing equipment and the flash zone due to the friction created by the passage of the vapors through the bubble caps and the liquid on the trays. The pressure drop between the vacuum producing equipment and the tower flash zone is further increased by the presence of steam normally introduced into the vacuum tower flash zone to lower the oil partial pressure and to assist in vaporization of the feed.

In addition to the steam normally introduced into the tower zone, steam or other stripping vapor is also introduced into the liquid oil present in the lower portion of the tower beneath the tower flash zone. This steam, referred to as stripping steam, is introduced to efiect final separation of lighter components from the higher boiling liquid oil. This liquid oil, referred to as bottoms, may comprise that portion of the heated feed oil which on introduction into the tower flash zone does not vaporize, but remains in the liquid state. r

The stripping steam introduced into the liquid bottoms, similarly as the steam introduced into the flash zone, causes a lowering of the partial vapor pressure throughout the liquid to such an extent that the light ends contained in the bottoms will be vaporized. The passage of these light ends and the stripping steam upwardly, together with vapors from the flash zone, through the fractionating zone (which is the practice in conventional operations) adds further to the pressure drop existing between the vacuum producing equipment and the tower flash zone, due to the increased friction resulting from the increased volume of rising vapors. The pressure. difierential between the top of the tower, where the vacuum producing equipment is most effective, and the lower portion of the tower is a factor which should be kept to a minimum for maximum vaporization. The higher pressure which conventionally exists in the stripping zone increases the requirements of stripping steam which must be used in this zone. The additional steam used to effect the stripping, when mingled with stripped light end vapors further increases the burden on vacuum producing apparatus due to the further increased pressure drop between the overhead line and the stripping zone.

It is an object of this invention to provide a vacuum distillation process and apparatus by which the pressure drop between the upper portion of the vacuum tower and the stripping zone is substantially reduced. I

A more limited object is to provide a process and apparatus accomplishing the above object, while at the same time providing additional structural support to the tower.

It is a further object to provide an improved process and apparatus which will accomplish the foregoing objects, while at the same time reducing the residence time in the tower of the stripped liquid.

It is still a further object of this invention to provide a vacuum distillation process and apparatus which will produce a greater amount of total overhead product, and which will also provide an improved rate of increase in total overhead, upon the introduction of additional stripping steam, over that produced by conventional vacuum distillation apparatus using the same additional quantity of stripping steam. Other objects will be apparent from the following description.

These and other objects are accomplished by my invention which comprises introducing a preheated liquid-containing feed into a flash zone, passing vaporized constituents from the flash zone upwardly into the bottom of a fractionating zone, and passing these vapors through the fractionating zone in countercurrent contact with downflowing condensate. Unvaporized liquid from the flash zone is passed downwardly through a stripping zone in countercurrent contact with stripping vapor flowing upwardly therethrough. Stripped and stripping vapors are passed direct- 1y from the stripping zone into the fractionating zone substantially above the bottom thereof, whereby the pressure drop between the top'of the fractionating zone and the stripping zone is reduced substantially. The path of flow of the stripped and stripping vapors in one embodiing zone and thus throughout each of said zones.

Unvaporized liquid is removed from the bottom of the stripping zone, and fractionated material is removed from the fractionating zone. The invention also includes apparatus for carrying out the process.

Figure 1 is a diagrammatic view of one preferred form of the vacuum distillation apparatus of this invention.

Figure 2 is a diagrammatic view of another modification of this invention.

Figure 3 is a graphic plot of total overhead against pounds steam/hour illustrating the improvement achieved by the invention.

Referring to Figure 1 of the drawing, numeral 8 represents the shell of a vacuum fractionating tower having feed inlet line 2 in the side of the shell. For simplicity, the apparatus will be described in connection with the distillation of a petroleum oil. The feed oil, which is heated to a high temperature and partially vaporized by conventional heating apparatus, not shown, is introduced by way of oil feed line 2 into the flash zone 3 of the vacuum tower. The heated oil, on introduction into the tower flash zone 3, flashes; that is, part of the heated oil which has remained liquid in the heating apparatus instantaneously enters the vapor state. This flashing of the heated hydrocarbon oil is at least in part the result of the reduced pressure at which the flash zone is maintained and the temperature at which the feed oil is introduced. Reduction of pressure in the flash zone is accomplished by means of conventional vacuum maintaining apparatus, not shown, in association with overhead vapor recovery means, also not shown. The vacuum maintaining apparatus may be of any conventional kind such as a vacuum pump; however, the normally used barometric condenser and steam jet of the conventional vacuum fractionation system ispreferred.

Heated. feed introduced at inlet 2 and partly vaporized in flash zone 3 results in vapors which rise through vapor passageways through a series, of plates or traysA; Thetrays 4 are designed. to provide maximum liquid-vapor contact, and

may be of any suitable type such as the conventional bubble cap tray shown. Other equivalent means may be employed, as will be evident to those skilled in the art. Trays 4 are provided with weirs I to maintain the proper liquid level on the tray. Downcomers 5 are provided for various trays to remove overflowing liquid to the next lower tray. The lower portions of downcomers 6, together with associated Weirs I and accumulated liquid condensate, provide vapor seals between adjacent trays.

In the operation of the tower it will be understood that hot rising vapors are in countercurrent contact with liquid having nearly the same composition. The liquid on each tray is at about its boiling point; consequently, when contacted boiling components and the liquid progressively rich in high boiling components.

As the vapor-liquid countercurrent contact continues in the tower, the liquid is separated out in the respective trays 4 according to its boiling point. Side-streams may be removed from-any particular tray by;means of draw-off lines such as 1ine'9. Side-streams thus removed can be subjected to further processing or treatment, as desired.

In addition to the side-stream or streams mentioned above, a recycle stream 10 is withdrawn from pocket H of the bottom tray of the series. This recycle stream withdrawn by way of line [0, is recycled into a heateignot shown, and thence into the flash zoneof the tower with the main oil feed.

Below the flash zone 3 is thestripping zone 24. The stripping member comprises a hollow, perforated, frusto-conical stripping member 28, mounted base upward, and connected to the flash zone 3 through a liquid trap or seal created by accumulated liquid from flash zone 3, together with flange 26 and weir 21. This liquid trap constitutes means permitting downflow of liquid from flash zone 3 into stripping zone 24, and prohibiting vapor interflow.

The stripping. element 28provides an improvement over conventional stripping means in that the structure employed provides little resistance to liquid flow. Accordingly, passage of unvaporized materialthrough the stripping zone is accomplished quickly without appreciable sacrif ce in stripping eiliciency. The decrease in residence time for the tower bottoms is advantageous, since a, higher temperature may be maintained in. the tower without thermal decomposition of the bottoms.

Frusto-conicalmember 28 is provided with av plurality of relatively small, substantially uniformly spaced perforations, which are adapted to form the stripping steam into a plurality of jets and'to direct saidjets upwardly and toward the center or vertical axis of the stripping section. The aforesaid gas jets operate immediately to distribute substantially all'liquid finding its way to the upper surface ofmember 2.8 into minute droplets of: largesurface areas. Accordingly, liquid to be stripped is quicklyandthoroughly contacted with av relatively'large quantity ofstripping vapor in, a. short period of time. The surface of member 28 is therefore substantially free of liquid during. operation.

.Desirably, the angleof the upper surface of member 28 with the horizontal is greater than the angle of repose of solids encountered in the tower bottoms. By virtue of this expedient the stripping section is self-cleaning.

The member 28 is also provided with a hollow, cylindrical drain leg 30 attached to its open, lower end. Leg 3ii'is adapted to direct the liquid from which lighter ends have been stripped into bottoms accumulator 3i. Leg 30 extends nearly to the bottom of accumulator 3i and is of slightly less diameter than the latter. Outlet line 32 is provided at the base of the bottoms accumulator 3|, by means of which stripped bottoms may be removed.

It will be noted that bottoms accumulating compartment 3| is of a cross-sectional area equal only to a fraction, e. g., between about 0.05 and about 0.5 of the cross-sectional area of the tower. This constitutes a substantial reduction in the side of the bottoms accumulators normally employed. As a result the residence time of the bottoms in the stripping zone is further decreased. The design limits of the size of the bottoms accumulator 3| vary according to the type of charge and particularly according to the amount of tower bottoms produced from the charge.

Numeral 25 refers to a frusto-conical stripping zone cap, positioned base downward, and having a maximum diameter slightly greater than those of members 21 and 28. Cap 2.5 effectively divides the stripping zone from the flash zone. Cylindrical flange 26 is attached to the lower end of member 25 and overlaps weir 21 to form a liquid trap or seal, referred to hereinafter.

Connected to the upper end of stripping zone cap 25 is a vapor tube or pressure equalizing conduit 23. The conduit 23 is of relatively small diameter, e. g., of the order of 2 or 3 per cent of the tower diameter.

The diameter of conduit 23 should be sufficiently large to carry 01f vapors and stripping steam from the stripping zone 24 without an appreciable pressure drop. Vapor conduit 23 should be of sufiicient length to extend into the fractionating zone, preferably as near the top as practicable, to permit the operation of the stripping zone at substantially the same absolute pressure level existing in the upper portion of the fractionating zone. Conduit 23 in Figure l is preferably positioned approximately in the center of the fractionating tower and is attached to the fractionating trays through which it passes. Through this expedient, it will be seen that conduit 23, in addition to serving as a pressure equalizing conduit, also acts as a tray support, thus providing increased structural strength to the tower and trays. Although the vapor conduit is preferably positioned centrally of the tower for the reasons indicated, many important advantages are still achieved where the vapor conduit passes externally or other than centrally of the tower from the stripping zone to a fractionating zone.

Although in Figure 1, as preferred, vapor conduit 23 extends from the stripping zone to the compartment immediately below the top tray, conduit 23 may be of longer or shorter length. However, tubes of shorter length are less desirable, since the advantages produced thereby are proportionately less. Normally, it is preferable for the vapors discharging from the upper end of conduit 23 to be contacted with condensate, prior to entry into the top of the tower. For this reason, it is usually desirable that conduit 23 terminate short of the top of the fractionating section. v

The connection between the flash zone and the stripping zone shown in Figure 1 comprises ,a liquid trap or seal created by accumulated liquid from flash zone 3 and by flange 26 (part of the stripping zone cap 25) and by weir 21. The liquid seal provides a means for permitting liquid hydrocarbons to pass from the flash zone into the stripping zone without passage of vapors from stripping zone 24 into flash zone 3 or in the reverse direction. Other sealing means may be employed. With the seal as shown, liquid from the flash zone moves downwardly to the inside of tray 28 toward the bottoms accumulator 3i. Stripped bottoms are removed from liquid accumulating compartment 3| by way of line 32. Y

Stripping steam is introduced into the stripping zone from line 12 through line l8. Valve I1 is provided on the stripping steam feed line to control the amount of steam. The quantity of stripping steam used depends on. the composition of the bottoms and the degree of vaporization obtained in the flash zone. The stripping steam introduced into the stripping zone removes lower boiling components from the liquid bottoms and passes upwardly with these light components through vapor conduit 23, into the upper portion of the tower.

Steam may be introduced into the flash zone from line l2 through line l5, if desired. A valve I3 is provided in the steam line l2 to control the amount of steam introduced into the flash zone. The amount of steam introduced into the flash zone (where this expedient is used) depends on the composition of the feed, the temperature of the feed and the pressure in the flash zone.

While it is possible to operate the tower without the introduction of steam into the flash zone, normal operations include the use of steam.

Figure 2 is a schematic representation of another vacuum fractionating tower embodying the principles of the invention. The illustrated apparatus of Figure 2 differs over that shown in Figure 1 merely in that a conventional bubble cap tray stripping section 50 is employed. In Figure 2 stripping steam from line 12 passes through valve l1, through line l8, and into the bottom of stripping section 50. The steam passes upwardly through the series of bubble cap trays 5! in countercurrent contact with liquid flowing downwardly across trays 5 I.

Liquid overflow from each of trays 5| passes to the next lower compartment by way of downcomers 54. A vapor seal is provided between adjacent compartments by the accumulated liquid in each downcomer and its adjacent weir 52. Stripped liquid collects in bottoms accumulating compartment 63 and is removed through line 62.

Stripping vapor and vaporized components pass upwardly through vapor conduit 23 as previously described. The flash section, the fractionating section, overhead product recovery system, etc., for Figure 2 operate similarly as correspondingly numbered elements of Figure 1.

In the normal operation of vacuum fractionating systems, the introduction of additional quantities of stripping steam produces a greater yield of overhead at the expense of the bottoms.

However, the additional steam used increases the pressure drop through the tower and the load on vacuum apparatus. The amount of additional stripping steam which may be used in conventional systems therefore is limited by the amount of the pressure drop resulting from such addition.

The tower provided'by this invention, however, substantially overcomes thisdifiiculty and avoids the increased pressure drop created by additional amounts of steam. The invention therefore permits the use of additional amounts of stripping steam without the. normally present disadvantages. Moreover, as will be readilyzapparent from Figure 3 of the drawings, and the. table 1 below, the introduction of additional quantities of steam into the tower'of this invention produces an unexpected rate of increasein total overhead, as compared with the addition of the same quantity of additional steam into the stripping zone of a conventional tower. The table 1 presents comparative figures illustrating the increase in total overhead yield obtainable by the invention as compared to the ields obtainable with a conventional tower (having, no pressure equalizing conduit) using the same quantities of steam.

It will be understood by thoseskilled in-the art that the invention isnot limited to the particular structure shown in the drawings, that various types of reflux may be provided, and that certain other conventional variations of vacuum distillation systems may be utilized.

Among the advantages produced by the invention are the increased production of total overhead products and the reduction in vacuum tower bottoms. Also, themodification disclosed in Figure 1 ofthedrawings is of particular advantage in that the maximum permissible temperature within". the tower may be increased without increased thermal decomposition. A further advantage of the invention is the increase in stripping steam permitted'without unduly overburdening the vacuum producing apparatus. Signiflcantlythe rate of increase in total overhead products is also improved with increased quantities of stripping steam. A further advantage resides in .the simplicity and economy of construction. Another important advantage re- TABLE 1 T tl Add gifemn' o a iin overi igfg Recycle, tower tional 2 d head (0) B./H. charge, steam. E Bottoms, minus BJH. ]bS./l1r. BJH. (B),

BJH.

A-Base operation 616. 5 154.5 681. 0. 347. 3 5, 840 401. 8

B-Conventioual tower 616.5 64. 5 681.0

545 357. 5 15,840 447.3 O-New tower 616. 5 644 5 0 1 f 2 v x 545 380. 7

1 Values plotted in Figure 3.

From the figures presented in table 1, it will be obvious that a given amount of stripping steam in a tower embodying the invention produccs a substantial increase in the total overhead, at the expense of the tower bottoms. Further, reference to Figures-indicates thatas the additional steam approaches about 1600 lbs/hr; above base operation, the rate of increase in overhead-is rapid. Where the increment of steam above base operation steam is above about 1060 lbs./hr., the total overheadproduct continues to increase to a limit, but the-rate of increase in overheadis reduced. It is therefore'more effb cient to operate with increments of steam producing the greatest rate of increase in overhead. However, such values may be exceeded substantially, where maximum recovery of overhead is desired.

The invention is advantageous inconnecticn with the vacuum distillation of any liquid mixture, particularly those containing constituents subject to thermal decomposition at normal distillation temperature. By way of example, the invention is suitable for the vacuum fractionation of topped crude petroleum to produce a clean cracking stock. Although the invention is particularly suited to increased production of catalytic cracking stock, it may also be used in the production of pressurestill stock for thermal cracking op erations,;ior the redistillation of'pressure distillate, pressed distillate, or bright stock solution. The invention may also be used to reduce'a tar stock to asphalt or'pitch. Itv is understood that the greatest value of theinvention is in. connection with those processes where the maximum amount of vaporization isdesired at the expense of the bottoms.

sides in the increased structural strength of the tower.

Although certain specific modifications of the invention have been described and shown, it is understood that various. alterations may be made Without departing from the spirit of the invention.

What. I claim is:

1. A vacuum fractionation process comprising introducing preheated liquid-containing feed into a flash zone, passing vaporized constituents upwardly into the bottom of a frac'tionating zone, passing these vapors through the fractionating zone in countercurrent contact with downflowing condensate, passing unvaporized liquid from-the flash zone downwardly through a stripping zone in countercurrent contact with upflowing stripping vapor, passing stripped and stripping vapors directly from the stripping zone into the fractionating zone substantiaily above the bottom thereof whereby the pressure drop between the top of the fractionating zone and the strippingzone is reduced substantially, maintaining a partial vacuum at the top of the fractionating zone and thus throughout the other zones, removing unvaporized liquid from the bottom of the stripping zone and removing fractionated material from the fractionating zone.

2. The process or claim 1 where the stripping vapor is directed upwardly and toward the center of the stripping zone in the form of a plurality of jets.

3. A process for the vacuum distillation ofnormally liquid mixtures comprising introducing preheated liquid feed into a flash zone, passing vaporized constituents from the flash zone upwardly through a series of vertically spaced frac- 4 tionating zones in countercurrent contact'with whereby the pressure'drop between the top ,of the fractionating zone 'and the stripping zone is reduced substantially, maintaining a partial vacuum at the top of the fractiontingl zone, and

thus throughout the other zones, removing unvaporized liquid from the bottom of the stripping zone, and removing fractionated material from the fractionating zone.

4. The process for the vacuum distillation of normally liquid mixtures comprising introducing preheated feed into a flash zone, passing vaporized constituents from the flash zone upwardly through a series of vertically spaced fractionating zones in countercurrent contact with downflowing condensate, passing unvaporized liquid from the flash zone downwardly through a stripping zone in countercurren-t contact with stripping vapor flowing upwardly therethrough, maintaining a liquid seal between the flash zone and stripping zone to prevent interflow of vapor, passing stripped and stripping vapors directly from the stripping zone into one of the fractionating zones above the lowermost in the series, whereby the pressure drop between the top of the fraotionating zone and the stripping zone is reduced substantially, said passage of stripping and stripped vapors being directed in a path positioned substantially centrally through the fractionating zones, maintaining a partial vacuum at the top of the fractionating zone and thus throughout the other zones, removing unvaporized liquid from the bottom of the stripping zone, and removing fractionated material from the fractionating zone.

5. The process of claim 4 where the stripping and stripped vapors are passed directly from the top of the stripping zone to the fractionating zone just beneath that topmost in the series.

6. Vacuum fractionating apparatus comprising a tower, means in the upper portion thereof forming a fractionating section, means in the lower portion thereof forming a stripping section, means for introducing stripping vapors into the stripping section, a compartment within the tower between the fractionating section and the stripping section forming a flash section, means for introducing preheated feed into the flash section, means forming a vapor passageway between the flash section and the bottom of the fractionating section, means at the bottom of. the flash section forming a connection with the stripping section and adapted to permit flow of liquid from the flash section to the stripping section, a vapor conduit connected to I the stripping section and adapted to discharge into the fractionating section substantially above the bottom thereof, means in association with the top of the tower for maintaining a partial vacuum therein, means for removing unvaporized liquid from the bottom of the stripping zone and means for removing fractionated material from the fractionating section.

7. The apparatus of claim 6 including means in the stripping section for forming stripping vapor into a plurality of jets and for directing said jets upwardly and toward the. center of the stripping section.

8. Vacuum fractionating apparatus comprising a tower, a series of vertically spaced fractionating sections positioned in the upper portion thereof, a stripping section positionedin the lower portion of said tower, a flash section positioned intermediately ofsaid stripping and fractionating zones, means permitting upward passage of vapors from the flash zone into the lowest fractionating section in the series, means permitting downward passage of liquid fromeach 'fractionating section to that next lower in the series, means forming a liquid trap permitting downward passage of liquid from the flash section into the stripping section and preventing interflow of vapor therebetween, a vapor conduit connecting the top of the stripping section directly to one of the fractionating sections above the lowermost in the series, means for withdrawing fractionated material from the fractionating section, means for introducing preheated feed into the flash section, means for introducing stripping vapor into the stripping section, means for withdrawing tower bottoms from the bottom of the stripping zone, and means in association with the top of the tower for maintaining a partial vacuum in said tower.

9. The apparatus of claim 8 wherein the vapor conduit is positioned substantially centrally of said tower and passes through the flash section and a portion of tbe fraotionating sections.

10. The apparatus of claim 8 wherein the vapor conduit extends into the fractionating section directly beneath the topmost section of the series.

11. The apparatus of claim 8 wherein the stripping section contains a stripping member comprising a hollow, perforated, frusto-conical member positioned base upward within the tower, and means for introducing stripping vaports between the tower and said frusto-conical member.

12. Vacuum distillation apparatus'comprising a tower, a series of fractionating trays transversely mounted within the upper portion of said tower and spaced vertically apart from each other. said trays being adapted to retain accumulated liquid on their upper surfaces, means permitting downward flow of excess liquid from each tray to that next beneath it in the series, a flash compartment within said tower beneath the lowermost fractionating tray, means for introducing preheated feed into said flash compartment, means permitting upward flow of vapors from said flash compartment through the series of fractionating trays and the accumulated liquid retained on their uppersurface, a stripping compartment-within said tower and positioned beneath said flash compartment, means permitting flow of unvaporized liquid from said flash compartment to said stripping compartment but preventing interflow of vapor, stripping means withment and a space above afractionating tray high in the tower, said conduit being attached to each fractionating tray through which it passbis-.meansin association with the top of the" tower iormaintaining partiatvacuum. in said tower. meansjor removing vaporsirom the space above thejtopmost fractionatingtray, means-for removing accumulated liquid 1mm the lowermost fractionating tray, means 1 for removing; at least one side-stream from an intermediate fractionatingtray, and'means forremoving unvaporized liquid from the bottom of said strippingeomnartment.

13. The apparatus of claim '12, including inadditiom-a liquid-accumulatingcompartment at the bottom .of the stripping compartment whose cross- -sectional areais 11118131210 tothe cross-sectional area 01 the tower. of between about 0.05:1 and about; 0.5 :1.

JOHN R. GUALA.

References Citedin the file 01 this patent UNITED STATES PATENTS Number Name Date 1,'25 7;470 Filippo Feb. 26, 1918 2,237,271 Dunham Apr. 1, 1941 2,358,272 Willkie Sept. 12, 1944 2,489,509 Straight- .Nov. 29, 1949 Miller July 3, 1951 

1. A VACUUM FRACTIONATION PROCESS COMPRISING INTRODUCING PREHEATED LIQUID-CONTAINING FEED IN TO A FLASH ZONE, PASSING VAPORIXED CONSTITUENTS UPWARDLY INTO THE BOTTOM OF A FRACTIONATING ZONE, PASSING THESE VAPORS THROUGH THE FRACTIONATING ZONE IN COUNTERCURRENT CONTACT WITH DOWNFLOWING CONDENSATE, PASSING UNVAPORIZED LIQUID FROM THE FLASH ZONE DOWNWARDLY THROUGH A STRIPPING ZONE IN COUNTERCURRENT CONACT WITH UPFLOWING STRIPPING VAPOR, PASSING STRIPPED AND STRIPPING VAPORS DIRECTLY FROM THE STRIPPING ZONE INTO THE FRACTIONATING ZONE SUBSTANTIALLY ABOVE THE BOTTOM THEREOF WHEREBY THE PRESSURE DROP BETWEEN THE TOP OF THE FRACTIONATING ZONE AN D THE STRIPPING ZONE IS REDUCED SUBSTANTIALLY, MAINTAINING A PARTIAL VACUUM AT THE TOP OF THE FRACTIONATING ZONE AND THUS THROUGHOUT THE OTHER ZONES, REMOVING UNVAPORIZED LIQUID FROM THE BOTTOM OF THE STRIPPING ZONE AND REMOVING FRACTIONATED MATERIAL FROM THE FRACTIONATING ZONE.
 6. VACUUM FRACTIONATING APPARATUS COMPRISING A TOWER, MEANS IN THE UPPER PORTION THEREOF FORMING A FRACTIONING SECTION, MEANS IN THE LOWER PORTION THEREOF FORMING A STRIPPING SECTION, MEANS FOR INTRODUCING STRIPPING VAPORS INTO THE STRIPPING SECTION, A COMPARTMENT WITHIN THE TOWER BETWEEN THE FRACTIONATING SECTION AND THE STRIPPING SECTION FORMING A FLAS SECTION, MEANS FOR INTRODUCING PREHEATED FEED INTO THE FLASH SECTION, MEANS FORMING A FLASH SECTION, WAY BETWEEN THE FLASH SECTION AND THE BOTTOM OF THE FRACTIONATING SECTION AND THE BOTTOM TOM OF THE FLASH SECTION AND ADAPTED TO PERMIT WITH THE STRIPPING SECTION AND ADAPTED TO PERMIT FLOW OF LIQUID FROM THE FLASH SECTION TO THE STRIPPING SECTION, A VAPOR CONDUIT SUBSTANIALLY ABOVE THE STRIPPING SECTION AND ADAPTED TO DISCHARGE INTO THE FRACTIONATING SECTION SUBSTANTIALLY ABOVE THE BOTTOM THEREOF, MEANS IN ASSOCIATION WITH THE TOP OF THE TOWER FOR THE MAINTAINING A PATIAL VACUUM THEREIN, MEANS FOR MAINTAINING A PARTIAL VACUUM THEREIN, MEANS FOR REMOVING UUNVAPORAND MEANS FOR REMOVING FRACTIONATED MATERIAL FROM THE FRACTIONATING SECTION. 